Method for sweetening hydrocarbons



Jan. 20, 1953 R. M. LOVE 2,626,232

METHOD FOR SWEETENING HYDROCARBONS Filed July 16, 1949 I I I I I I I I I I I CORROSION OF MILD STEEL BY 0,0035 AQUEOUS HYPOCHLORITE SOLUTIONS PENETRATION vs FREE N OH I l I SEVERE FITTING m KMODERATE FITTING 3 0.0025 n: i

m ll] 5 z 0.0020 2 9 1 I 0.0Ol5 u SEVERE FITTING NO PITTING\ NO FITTING it 3O 4O 5O 6O 7O 80 90 I00 "0 I 130 I I I I I FREE N OH GRAMS PER LITER 2f BY O m.

Patented Jan. 20, 1953 METHOD FOR SWEETENING HYDROCARBONS Robert M. Love, Baytown, Tex., assignor, by mesne assignments, to Standard Oil Development Company, Elizabeth, N. J., a corporation of Delaware 4 Application July 16, 1949, Serial No. 105,136

5 Claims. (Cl. 196-29) The present invention is directed to a method for sweetening hydrocarbons. More p u y, the invention is directed to an improved method of sweetening sour petroleum distillates and in its,

more specific aspects is directed to sweetening sour petroleum distill-ates having a boiling point no greater than 700 F.

Prior to the present invention it has been known to sweeten hydrocarbons and particularly sour petroleum distillates with alkaline hypochlorite solutions. However, the methods of sweetening sour hydrocarbons with alkali metal hypochlorite solution as taught in the literature have many disadvantages. The process of the prior art is uneconomical because the sweetening agent is partly consumed in reactions other than sweetening. Another great disadvantage is that the prior art solutions have been exceedingly corrosive to steel equipment in which the treating procedures have been carried out. Besides the above disadvantages, the naphtha is chlorinated, which is undesirable. Furthermore, the power- Iful oxidizing tendency of hypochlorite causes any hydrogen sulfide present in the naphtha to be converted to free sulfur, which in turn causes the sweetened naphtha to fail to pass the copper strip corrosion test.

It is, therefore, the main object of the present invention to provide an improved sweetening process in which the disadvantages of the prior art are substantially eliminated.

Another object. of the present invention. is to provide an improved alkaline hypochlorite treatingreagent which is substantially non-corrosive to steel equipment and which does not deleteriously afiect hydrocarbons sweetened therewith.

A further object of the present invention is to provide an improved alkaline hypochlorite treating reagent in which the tendency toward undesired reagent consuming reactions is reduced to a minimum.

A still further object of the present invention is to sweeten sour petroleum distillates having boiling points no greater than 700 F. with a hypochlorite solution which does not cause chlorination of the naptha.

It has now been discovered that contrary to the teachings of the prior art, improved results may be obtained by employing alkaline hypochlorite solutions containing in excess of 90 grams of free alkali metal hydroxide per liter in sweetening hydrocarbons having boiling points no greater.

than 700 F.

Thus, the present invention may be briefly de-,

scribed as involving the contacting of a sour hy-;

drocarbon boiling up to 700 F. with an alkaline, hypochlorite solution such as one containing sodium hydroxide in excess of 90 gramsof free sodium hydroxide per liter and available chlo-;

rine in excess of 1 gram per liter. The sour hydrocarbon and the alkaline hypochlorite solu-. tion are contacted intimately, separated and the sweetened hydrocarbon recovered. The sweetened hydrocarbon may be subjected to a washing operation with water to remove any hypochloritewhich may be suspended or entrained therein. 7

The temperature, at which the treating operation in accordance with the present invention may be conducted, may range from about 40 up to about 120 F. with temperatures in therange from to 90 F. being preferred. When sweetening sour volatile hydrocarbons it may be neces-. sary to superimpose pressure on the treating equipment to maintain the hydrocarbon in the; liquid state. a

The alkaline hypochlorite solution employed in the practice of the present invention may be prepared by any one of the Well known methods of preparing hypochlorite solutions. A convenient method of preparing hypochlorite solution is, merely to bubble chlorine gas into a solution of alkali metal hydroxide such as sodium hydroxide of proper strength to make the hypochlorite. While sodium hydroxide is the preferred alkali metal hydroxide, by virtue of its availability, it is within the scope of my invention to use other alkali metal hydroxides in lieu of sodium hydroxide; for example, potassium hydroxide and lithium hydroxide may be employed in the prac-' tice of my invention.

The type of hydrocarbon which may be treated in accordance with the present invention may range from the liquefied petroleum gases such as propane and butane up to and through sour hy-" drocarbons in the heating oil boiling range. For example, besides propane and butane, the hydrocarbons in the gasoline boiling range boiling from about up to about 450 F., the hydrocarbons in the kerosene boiling range and those in the heating oil boiling range including hydrocarbons boiling up to about 700 F. may be sweetened in accordance with the practice of the present invention. These hydrocarbons may be obtained from crude petroleum or from conversion operations such as thermal or catalytic cracking operations, and the like. Prior art workers have been unable to sweeten cracked stocks but my reagent may be successfully employed in sweetening such fractions.

The treating operation in which the hydrocarbons are contacted with the alkaline hypochlorite solution "may be conducted in any one of several ways. For example, the alkaline hypochlorite and the sour hydrocarbon may be contacted by admixing the treating reagent and the .hydrocarbons in mixing pumps, incorporators, vessels equipped with stirring devices such as propellers, and the like, constructed of ferrousimetals .or by jetting the sour hydrocarbon into a pool ofalkaline hypochlorite solution. Mixin may be accomplished by circulating the alkaline hypochlorite solution and the naphtha from one vessel to another. Contacting may also be obtained countercurrentl in a suitable contact tower equipped with equipment such as cascade trays, bell cap trays, and the like. There are many admixing devices on the market which may be used in the practice of the present invention. It is a feature of the present invention that my improved :process and reagent may be used in ferrous metal equipment without destruction thereof.

Inorder toillustrate the invention further, sour kerosenes hav-ing copper numbers of "38 and 66, respectively, were treated with hypochlorite solutions containing available chlorine and free sodium hydroxide in amounts disclosed in the literature. The hypochlorite solutions and the sour kerosene were intimately contacted, separated after treatment and the treated kerosene subjected .to tests. 'The'resultsof these tests are given in .the followingttable TABLE I HypochZori-te sweetening of sour 'kerosenes '4 rite solutions containing variable quantities of available chlorine and free NaOI-I for periods ranging from 19 to days. The steel specimens, prior to immersion in the hypochlorite solution, were weighed and after the period of immersion stated were removed, washed and reweighed to determine the metal loss. Visual observations of the steel specimens with respect to the attack of the metal by the hypochlorite were also made.

It will be noted from the data given in Table II that thehypochlorite solutions containing 83 and less grams of sodium hydroxide .per liter showed marked effect in corroding the specimens of steel .as evidenced by severe pitting. It will be noted that there seems to be no correlation of the efiect of the available chlorine-on corrosivity of the hypochlorite solution to the metal.

Besides the deleterious effects mentioned before, as shown by the data in Tables I andII, it has :been found that hypochlorite solutions containing less than .90 grams of sodium hydroxide per liter when contacted with petroleum distillates-containing H25 result theHzS being converted to free sulfur which is well known to be detrimental to hydrocarbons .to be employed as solvents, or as .fuels.

In order .to illustrate the practice of the present invention, asour kerosene having a copper numbe1vof38 was contacted with hypochlorite .solutions containing approximately 92, 139 and 700 grams 0f free sodiumhydroxide per liter. The amounts of available chlorine in these solutions ,flypomorfie were 11.7, 39.2 and 7.5 grams per liter respecsollltjililtl, o Hypochloritetreat I R Sid l tively. Aitersep-aration of thehypochloritefrom ggs; Doctor. ,g gg; the sweetened kerosene the kerosene was tested 1 or test of and the following results were obtained:

Avail. F chtarlgie V1 'stolghiotreatlegd I ree s cc 0. *me ric s 00 F311: NaQH. percent cquiva- TABLE III sweetening ofsour kerosene with high-alkalinity h .ociilor'z'te oluti n 10.2 "26 88 25 6.0 Neg 2.19 8 o 10.f2 '26 66 25 5 N 3; 28 Zaution, Hypochlorite treat 111.12 2 :66 0 7. Beg i5? :gmsllit. ".(lopger Residual It W111 be apparent from the data in the ,forefig}? .Ftee stock 7 vol. metric it? 1 oing Table I and specifically from the number 01, I NaOH Percent. 5;?

of lstoichiometric equivalents of reagent required to obtain a doctor sweet product that aconsider- 11.2 92,2 38 M 1 66 Neg 0 30 able number of side reactions were taking place 5 39.2 1s9-0 38 at 1.85 Neg: Z20 in-the solutions made up in-accordance with the prior art. [It will be apparent further that these side reactions consume hypochlorite and make the process quite expensive. The high residual acidities of the treated naphtha indicate chlorination-of the naphtha is taking place, which is undesirable.

.In order to demonstrate the corrosiveness of the hypochlorite solutions of the prior art to steel, steel-specimens were immersed in hypochlo- Mls. of- 0.10 N KOH per mls. of treated stock.

5 treated stock: is approitimatelyi onc -tenth or that shown in -Tablaland particularly where the-cop-- pennumber' or the feed stock was the" same. With the" high' 'cop-per number 'stocki-t will be'apparerit that 'the reSidn-aI acidity-in one casewas approxi matelyi one twen-tiethor that shown when the prior art reagents were employed.

In orderto determine conclusively the superior itytof the treating solutions of the presentinvention over the prior" art solutions, the sour kero series used in obtaining; the data of Table I were treated as in the examples of Table- I with hypochlorite solutions containing available chlorine andtfree sodium hydroxidein amounts disclosed in the literature. Smaller amounts of reagent were usedthen :inthe 'examplesof Table-L After contacting. the sour kerosene and sweetening agent; and recovering' the' treated' herosenegz it was tested and the-' followingresultswere obtained TABLE IV" unable mi fa Voluriie' S'toicliio'met'ric hector Ola NaOH 5 percentequivalents test 10.2 26 3,8 10 2 4 P cs. 9.- 2 ,2 3 l0. P0 10:2 2 66 3. 5 P05.

It will'b e apparent from this foregoing data that quantities of the riorart sweetenin soluti ohs amounting to -2'.4=--3.5 stoichio'rne'tric equiv alents' failed top'roduce" doctor sweet products; It will be apparent also that the-amount of the prior art sweetenin solution used in these examples was 13' to" 2&7 times the amount of my improved sweetening solution'which' was used in the examplesof Table" II-I in' which do'ctorsweet products were obtained;

In order to illustrate the non-corrosivity of the solutions employed in the practiceoi the present invention, specimens of steelsimilar to that described in the preceding examples were immersed in hypochlorite 'solutionscontaining. in excess of 96 grams of free so'dium'hydroxide per liter. Thesevveighed specimens remained in the hypochlorite solution for periods of timera'nging from 19- to 25 days, after which they were "removed from the corrosive solutions, washed with water,--dried and reweighed; the metal loss was calculated'as inches per year. In addition, the condition of the metal was observed to-determine whether or notit had. become pitted. These results-aretshown in Table V as-followsz TABLE v steelsfiipcorrosioatet's'oj nigh alkztZinityhypochlorite solutions Comparing these results" with those shown in Table II it will be immediately apparent that the solutions of the present invention give substan tia11 y improved results;

'l'he reature's' or the presentinventionwilt-he 00 single figure inwhich the datapresented in Tables I; and V areplotted'. The amount "of tree'sodium hydroxide in grams per liter has been; plotted again'st thecor-rosion reported "inchesperyear. By'reference to the dfawing it 1' be" seen that-at 83 grams of free NaOH" per Iiter onl moderate pitting occurred; 'I hisamountof free NaOH the'h ypochlorite solution resulteci in a pone trationof 0.0028 inch per year'ofthe steel specimen. Furthe'r reference wi11' snow" that" at 96- grams of" freeNaoH per liter the corrosion rate wasocoo2 in'chperyear. lt wnl be apparent that the-hypo'chlorite solution containing 83 grams per l-ite'r of f e NaOH caused moderate: pittingof the steel specimensinceoniy mode "te 'pitting occurred at 8'3 ramsor f-ree" NaOH per-l1ter and no pitting-*oceurredwhen a solution containing 96 y nonmorrosive to steel and that these solutions may be safely used in steel equipment' ih-which the-treating reaction iscondueted Besides the solutions of the present invention being" nonworrosive, non-reactant with the naphtha and inexpensive" to employ, theyals'o' do not'convert hydrogen sulfide to free su'lfu'rl It was found that 'free sulfurwas not formed when solutions containing 96 grams of free NaOH per liter were employed in treating" naphtha containin'ghydro'gen sulfide.-

A number of runs were made in which a mix ture of cracked and crude petroleum naphtha was contacted with a hypochlor'ite'solution containing 10 grams of available" chlorine per liter of reagent and 139 "grams of sodium hydroxideper liter of reagent. The'naphtha'had a copper number of 6 and was contacted with 2, 3 and 4 volume per cent of the reagent. The s'toichidmetric equivalents of hypochlorite employed in the different treats were respectively 3, 4%; and 6. After the naphtha'had been contacted with the solutions in the various amounts, the reagent was separated therefrom, washed with water and the treated naphtha tested for copper number. It was found that the copper number of the naphtha treated with 2 volume percent of the reagent had been reduced from 6 to 2; while the naphtha treated with 3 volume percent of the solution had a copper number of 1, areduction of 5 units. The naphtha contacted with -volu-me-percent of the hypochlorite solution mentionedbefore was doctor sweet as indicatedby; the'atorementioneddoctor test.

A high sulfur refined oilwhich was a sulfur dioxide extractof a kerosene fraction was then treatedwith the same hypochlorite solution,--runs beingmade with 5,19,12 and-13 volume percent of the reagent.- In these-runs-t-he stoichiometric equivalents of hypoch-lorite employed were respectively 03,-1.6, 1.9 and 2. 1. After the reagent had been separated from the treated solvent extract, washed with water, the solvent extract was tested for copper number and-was found to have copper numbers of 29 1 0, less-than 1 and finally the one contacted with '13 volume percent passed the doctor test. It will be apparent from these data that a marked reduction in copper number is obtained by using small quantities of the treating" reagent (iftln'epresent invention and furthermore it is possible to obtain" a completely sweetened product.

It is possibleto employ 'vens'rnaller quanta: ties of re gents than those employed-in thefore= going examples; If itis desired to usesmaner evenmore apparent reference the quantities, the amount of reagent may be decreased by employing a hypochlorite solution containing greater amounts of available chlorine than shown in the preceding examples. As an illustration thereof, the foregoing high octane number naphtha having a copper number of 6 was contacted with a hypochlorite solution con-' taining '75 grams of available chlorine per liter of reagent and containing 140 grams of sodium hydroxide per liter. The high octane naphtha was contacted with 0.25, 0.5 and 0.6 volume percent of reagent which amounted respectively to stoichiometric equivalents of hypochlorite of 2.8, 5.6 and 6.7. After contacting with these amounts of the reagent the reagent was separated from the treated naphtha and the copper number of the treated naphtha after washing was determined and found to be respectively 2.5, 0.5 and the last sample was doctor sweet. It will be noted that the stoichiometric equivalents of hypochloe rite in these runs were substantially identical to the stoichiometricequivalents of the previous runs indicating that the amount of treating reagent employed will depend to a large extent on the available chlorine in the hypochlorite solution.

Similar results may be obtained with the aforementioned solvent extract when employing a hypochlorite solution containing '75 grams of available chlorine per liter and 140 grams of sodium hydroxide per liter. In runs of this nature the volume percent of the reagent employed may be decreased from to 1 in one instance and from to 1 in another instance, while providing substantially the same stoichiometric equivalent of hypochlorite and obtaining substantially the same reduction in copper number. Specifically, sweetening may be obtained with the latter reagent employing 2.25 volume per cent of solution and a stoichiometric equivalents of hypochlorite of 2.7, whereas in the previous runs where 13 volume percent of the reagent having 10 grams per liter of available chlorine and 2.1 stoichiometric equivalents were necessary to ob-' tain a doctor sweet product.

From the foregoing it will be apparent that the treating reagent of the present invention should contain more than 90 grams of free alkali metal hydroxide per liter and may contain available chlorine in amounts ranging from about 1 to 150 grams per liter. It is specifically contemplated in the present invention that hypochlorite solutions may be employed containing free alkali metal hydroxide in the range from about 90 to 700 grams per liter and available chlorine in the range from about 1 to 150 grams per liter. Besides the naphthas mentioned specifically before, it is contemplated that the present invention may be applied to treatment of pentane and pentylene fractions, light naphthas from crude petroleum, thermally and catalytically cracked fractions, kerosenes and solvent naphthas. For example, the present invention has particular application to sweetening solvent naphthas such as one obtained from crude petroleum. Such naphthas boil in the range from about 300 to 400 F. and. may contain aromatic and naphthenic hydrocarbons besides a predominant amount of parafiins.

In order to illustrate the invention further a solvent naphtha obtained from a mixture of Texas crude petroleums was contacted with an alkaline hypochlorite solution containing available chlorine in the amount between 3 and 5 gramsper liter and free sodium hydroxide in the range between 100 and 1'70 grams per liter at a temperature ranging from about 80 to F. This solvent naphtha had a copper number of less than 1 and was sweetened in contact with the alkaline hypochlorite solution without excess consumption of reagent and without chlorination of the solvent naphtha. The naphtha was contacted with the hyprochlorite solution at a rate of about 14,000 barrels per day. The solvent naphtha treated in accordance with this procedure was found to pass a copper strip corrosion test which is the ordinary A. S. T. M. copper strip test modified to the extent that the copper strip is immersed in the naphtha for half an hour at its boiling point.

As shown by the several examples it is possible to treat the hydrocarbons in accordance with the present invention and to eliminate only part of the mercaptan content with the treating reagent of the present invention. It is contemplated that my invention may be used in connection with other well known treating processes such as for example the doctor sweetening process. In some instances it may be undesirable to sweeten completly, that is to reduce the copper number to where the naphtha passes the doctor test. In those instances hypochlorite solution might be followed by a treatment with doctor solution and the numerous equivalents thereof in the prior art. Conversely, the present invention might also be used in connection with other well known sweetening processes, for example in the treating process of the prior art where sour hydrocarbons are contacted with alcoholic solutions of alkali metal hydroxide, it might be desirable to follow such a treatment with the improved reagent of the present invention. Likewise the operation with the improved treating reagent might be followed by contact with the alcoholic solution of sodium hydroxide if desirable.

The nature and objects of the present invention having been fully described and illustrated, What I wish to claim as new and useful and to secure by Letters Patent is:

1. A method for treating petroleum distillates which comprises contacting in a ferrous metal container a sour petroleum distillate having a boiling point below 700 F. with an alkaline hypochlorite solution non-corrosive to said metal container containing in excess of grams of free alkali metal hydroxide per liter and available chlorine in the range between one and five grams per liter, removing said hypochlorite solution from contact with said distillate and recovering a sweetened distillate- 2. A method in accordance with claim 1 in which the alkali metal hydroxide is sodium hya droxide.

: 3. A method in accordance with claim 1 in which the alkali metal hydroxide is potassium hydroxide.

4. A method in accordance with claim 1 in which the alkali metal hydroxide is lithium hydroxide.

5. A method for treating petroleum distillates which comprises contacting in a ferrous metal container a sour petroleum distillate having a boiling point below 700 F. with a sodium hypochlorite solution non-corrosive to said metal container containing sodium hydroxide in an amount in the range between and 1'70 grams per liter and chlorine in the range between 3 and 5 grams per liter, removing said solution from contact with said distillate and recovering a sweetened Number Name Date distillate. 1,600,845 Reinhold Sept. 21, 1926 ROBERT M. LOVE. 2,488,855 Denton Nov. 22, 1949 2,550,668 Brandon et a1 May 1, 1951 REFERENCES CITED 5 The fo1 1owing references are of record in the OTHER REFERENCES me of thls patent Wood et aL, Ind. and Eng., Aug. 1926, pp.

UNITED STATES PATENTS 32346 (1926) Number Name Date Kalichevsky et a1., Ref. of Petroleum, pp. 212-13 1,552,830 Dunstan Sept. 8, 1925 (1942), 

1. A METHOD FOR TREATING PETROLEUM DISTILLATES WHICH COMPRISES CONTACTING IN A FERROUS METAL CONTAINER A SOUR PETROLEUM DISTILLATE HAVING A BOILING POINT BELOW 700* F. WITH AN ALKALINE HYPOCHLORITE SOLUTION NON-CORROSIVE TO SAID METAL CONTAINER CONTAINING IN EXCESS OF 90 GRAMS OF FREE ALKALI METAL HYDROXIDE PER LITER AND AVAILABLE CHLORINE IN THE RANGE BETWEEN ONE AND FIVE GRAMS PER LITER, REMOVING SAID HYPOCHLORITE SOLUTION FROM CONTACT WITH SAID DISTILLATE AND RECOVERING A SWEETENED DISTILLATE. 